Aeron Hodges is a small woman, but if she stretches out both arms she can embrace the whole kitchen in the compact “innovation unit” Mayor Menino is promoting to attract young workers to Boston’s newest neighborhood. Designed by the architecture firm ADD Inc, the apartment is sleek and sculpted, with cool features like convertible storage and a wall mount for the inevitable Geekhouse bicycle. It’s likely to be popular with young, single employees of the biotech and financial companies coming to the Innovation District, and with retirees looking for an urban pied-à-terre. What it is less likely to be, regrettably, is affordable.

A full-scale model of the micro unit — all 300 square feet of it — was on display recently at the Boston Convention and Exhibition Center. Hodges and her colleagues built the model in conjunction with Menino’s “ONEin3’’ initiative (named for the 30 percent of city residents who are between the ages of 20 and 34). “The most exciting part of the process is the collaborative nature of the construction itself,” she said, perfectly summarizing the culture of this demographic.

Over several months, the ADD Inc team asked young professionals what they would sacrifice to afford living downtown. Few wanted granite countertops or hardwood floors. Only 30 percent said they thought 300 square feet was too small; most would trade space for a shorter commute. They wanted to be close to public transit, hip restaurants, and their jobs.

These “creative economy” pioneers are redefining the relationship between public and private space. They want privacy for the essentials — bed and bath — but beyond that they are willing to share. The city is their living room. The local bistro is their kitchen.

ADD Inc senior associate principal Tamara Roy likens the micro unit to the Smart Car or Mini Cooper: products the auto industry recognized would appeal to people looking for affordability, good design, and a lighter environmental footprint. “Kudos to the mayor for encouraging developers to do a different housing model,” says Roy. “It increases supply and diversifies the market. But it’s not going to answer the affordability question.”

The units — often so small that Menino needed to exempt them from city codes — respond to changes in demographics and consumer attitudes. According to the annual housing report card by the Dukakis Center at Northeastern University, 12,000 new units a year are needed to meet projected population growth in metro Boston, and much of the demand will be in the city core.

The study’s author, Barry Bluestone, said housing starts will be driven by two groups at opposite ends of the demographic spectrum: older retirees with significant assets looking to downsize, and recent college graduates with significant debt. Both could be attracted to the new micro units. But one group can pay a lot more.

Fifty
mini units, which are closer to 450 square feet, are planned for the residential tower on the former site of Anthony’s Pier Four. There are no cost controls; the units will command whatever the market will bear. No one knows for sure, but estimates range around $1,500 a month. Reasonable? You’d need to earn $72,000 a year for that rent to be 25 percent of gross income, the usual goal.

As always with real estate, the issue is location, location, location. Land in the Seaport is expensive; construction is costly and difficult. “We should be thinking more broadly, beyond the waterfront,” said Bluestone. For now, however, the micro units are only approved for the Innovation District.

Before the housing crash in 2008, Boston’s political and business communities were united in pushing for affordable housing. The Chamber of Commerce listed high housing costs as a top impediment to economic growth. Then the collapse of the market gave some a false sense that prices would “normalize” in Boston. But they didn’t. According to Bluestone’s report, only New York and San Francisco outpace Boston in rental housing costs.

Just increasing supply won’t be enough. What is needed is a recommitment by government and the private sector, with cross-subsidies or direct housing stipends, if necessary, to keep the micro units below $1,000 a month. Otherwise the city’s hottest new neighborhood will be very small place indeed.

Renée Loth’s column appears regularly in the Globe.

Correction: An earlier version of this story incorrectly identified Tamara Roy’s position with Add Inc. She is a senior associate principal.